1. Field of the Invention
The present invention relates to an image formation apparatus.
2. Description of the Related Art
Ordinarily, at an image formation apparatus such as a printer or the like, sheets at which images are to be formed are accommodated in advance at a paper supply unit, such as a cassette, a magazine or the like, which is withdrawably mounted at an apparatus main body. The sheets are taken out one at a time by a feeding mechanism provided at the apparatus main body and are fed to an image formation section, and image formation is implemented. At such a time, in order for the sheets to be taken out by the feeding mechanism with conveyance characteristics being kept constant regardless of the number of sheets remaining in the paper supply unit, a structure in which a baseplate on which the sheets have been placed is urged toward the feeding mechanism by a compression spring or the like is common. However, when sheets are to be loaded, setting of the sheets is not possible unless the baseplate is moved away from the feeding mechanism.
Accordingly, a paper conveyance unit has been proposed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 11-343037) in which, when a paper supply unit is withdrawn from an apparatus main body, in order to facilitate setting of sheets, a lift plate on which the sheets are to be placed is pushed downward, against an urging force which urges the lift plate upward, by a push-down cam. Thus, the lift plate is put into a state such that it is possible to set the paper.
However, with a paper supply unit as described above, it is necessary for the push-down cam to be pushed up by a rotary cam at times of paper supply, and there has been a problem in that a rotary load of the cams is large. Moreover, in the state when the paper supply unit has been withdrawn, the lift plate is being pushed down by the push-down cam against the urging force which urges the lift plate upward. Therefore, if, during setting of the sheets, the push-down cam is removed from the lift plate for some reason, the lift plate will rise with great vigor and there is a danger of fingers being nipped or the like. Furthermore, if the rotary cam is offset from a proper position thereof for some reason, the rotary cam and the push-down cam may collide during insertion of the paper supply unit. Hence, since there is urging by the push-down cam, if the push-down cam has been specified so as to ride up on the rotary cam, resistance when the push-down cam rides up contributes to resistance to the insertion, and it may be more difficult to mount the paper supply unit at the apparatus.
Alternatively, a paper conveyance unit has been proposed (see, for example, JP-A No. 2002-154670) which has a structure in which: a raising/lowering member pulls up two sides of a free end of a baseplate provided in a paper supply unit, by force of extension springs; the raising/lowering member is provided in a space inside a grip which is formed at an end portion of the paper supply unit; a guide is provided at a paper supply aperture of a main body of an image processing apparatus and the guide includes a guide surface which inclines gradually upward in a direction into the paper supply aperture; and in a procedure of mounting of the paper supply unit at the paper supply aperture, a raising/lowering arm is lifted up by the inclined surface of the guide, and a leaf of paper on the baseplate is pressed against a paper supply roller.
In this example, in a state in which a cassette case is withdrawn from the paper supply aperture, the raising/lowering member is disengaged from the guide, and the baseplate is maintained in a declined state by its own weight. Therefore, sheets can be set thereat with ease. In the procedure of insertion of the cassette case into the paper supply aperture, the raising/lowering member is supported at the guide surface of the guide and gradually lifted up, so that the baseplate is raised by the force of the extension springs and the paper leaf is pressed against the paper supply roller.
However, in such a paper supply unit, since the guide is a fixed guide, it is inherently not possible to move up and down the baseplate after the mounting of the paper supply unit. Furthermore, the fixed guide takes up length, so more space is required in the direction of insertion of the cassette.